I started using a version of GIMP once my PS trial ran out. there is no .dds plug in for it but you can find converters that make .tga's into .dds's. both programs are free just search google for the programs

This submission is a graphics tool that generates DDS files (texture
format) in batch from a collection of popular file formats such as
BMP, PNG, PSD > and TGA. For this version, I selected nVidia's nvDXT
to produce them so the files produced by it are of the same quality
as they would be with > nVidia's DDS plugin for Photoshop.

The installation program will create shortcuts and add an entry into
the &quot;Add/Remove programs&quot; dialog box.